You'll need 10 of the weapon and 10,000 GP for the first level, 20 weapons and 20k for the second, 40 weapons and 30k for the third, 80 weapons and 40k for the fourth. When you have the weapons, you can Train for 50 AP:

You lose 10000 Gold Pieces.
You lose 10 Sais.
You train like anything.

Your base damage for that weapon is increased by 1 following training. Each weapon also gains a special property after the each training. For Sais it's another attack; for Bo staffs it's damage reduction like an iron bling; for Nun chucks it's another attack to the clockwise monster. You also gain the ability to safely attack ninjas with those weapons without risking disarming. Tars, on the other hand, will still happily devour your weapons.

Note that you won't necessarily damage the ninja. At least, they still dodged all the damage from my first-level trained nun chucks attacks. --Greycat 12:58, 14 August 2007 (BST)

I didn't get any increased accuracy with either Bo Staff or Sai training. The Bo Staff went from base 2 damage to base 4 (with only one level), but no change in accuracy (still at +40%, where it was initially). The Sai went from 2 damage/1 attack to 3 damage/2 attacks to 4 damage/3 attacks with no change in accuracy. --Dragon 07:40, 21 August 2007 (BST)

Out of four attacks (two staff, two nunchucks) I was able to connect once. I wonder if the likelihood of hitting the ninja increases with more levels -- Thog 14:52, 24 August 2007 (BST)